The platelet-Alpha-granule contains a number of specific proteins, including platelet factor Beta-thromboglobulin, platelet derived growth factor, and a PF-4 carrier proteoglycan (PG). Human PF-4 coupled to resin serves as an affinity matrix for the isolation of this PG. Binding studies using this PG indicate that it binds PF-4 but not Beta-TG; the PG has been localized in the platelet Alpha-granule fraction of sucrose gradient fractions of platelet lysates. The nature of the protein and carbohydrate portions of the PG will be established. PF-4 affinity resins co-purify a 70,000 dalton protein which is uncharacterized. This protein will be isolated and analyzed for chemical composition, PF-4 binding characteristics, and platelet release. Heparin can also be separated into three fractions using PF-4 affinity columns. The specific activities of these heparins will be evaluated using thrombin and factor Xa chromogenic substrates. Human Beta-TG affinity columns will be prepared in a manner identical to those used for PF-4. Platelet lysate material previously passed over heparin resins will be chromatographed on Beta-TG resin to ascertain whether there exists a class of Beta-TG specific binding proteins. Similarly, heparin will be chromatographed and compared with the activities obtained from PF-4 resin and also from antithrombin, protamine, thrombin and DEAE fractionated heparins. Peptide analogues to the carboxy-terminal regions of PF-4 will be evaluated for their anti-heparin activity. Using dextran sulfate resins, bovine platelet lysates will be fractionated and the amino acid sequence of the PF-4 completed. Bovine Beta-TG fractions will be assayed for mitogenic activity, using Balb 3T3 cells. Guinea pig megakaryocytes will be collected and maintained in liquid cultures for timed intervals of up to 5 days. Following pulse labeling, the labeled PF-4 and Beta-TG like proteins will be harvested, and their specific activity calculated to establish the time parameter of protein synthesis by the megakaryocyte. Animals pretreated with guinea pig platelet antiserum will be examined in an identical manner in order to determine the effect of thrombocytopenia upon megakaryocyte protein synthesis of Alpha-granule proteins.